Safety device for fluid brakes



Oct. 19, 1948, D. R. HERRIOTT 2,451,828

' SAFETY DEVICE FOR FLUID BRAKES Filed Jan. 6, 1947 A 2 Shets-Sheet 1 a1a 41 25 2:191:11 2a fi- 04 m9 2 #520077,

I N VEN TOR.

arrow/[s4 D. R. HERRIOTT SAFETY DEVICE FOR FLUID BRAKES Oct. 1 1948.

Filed 1947 2 Sl1eet 2 1941402- A/sp r I N V N TOR.

Patented Oct. 19, 1948 UNITED The invention relates -to a safety devicefor the fluid brakes on an automobile or the like, and has for an objectto prevent leakage in one of the brake lines or conduits from renderingall of the brakes inoperative. 5

The invention provides a safety device in the form of a piston to whichthe fluid pressure from the master cylinder is applied. and which inturn transmits-that pressure "to the fluid line leading to.

the brakes. A plurality of such safety devices are 10 employed, forexample one for the rear brakes, I

vide means operating in conjunction with the 29 fluid pressure toprevent the piston from dri-f ing to a-position closing thebrake port.

A further object ofithe inventionis to maintain the brake lines full offluid to offset incipient leakage or evaporation, without, thereby,causing the piston to drift towards the brake port.

A still further object of the invention is to-provide a hy-pass andbleed arrangement permitting the brake line and the cylinder of thepiston tobe bled through the piston. i

For further details of the invention, reference may be made to thedrawing wherein Fig. 1 is e; schematic view of the safety device ofthe-present invention. i

Fig. 2 is a full size view of the safety device in 3 side elevationpartly in section.

Fig. 3 is a sectional view on line 3 3- of Fig; 2.

Fi 4 is a sectional view on line 44 of-Figl 3.

The views in Figs 3 and 4 are taken in the di-;' rection of the arrows.F i

Fig. 5 is a viewin elevation, partly in section of a well-known brakesystem having the safety' device of this invention. I

Fig. 6 is a schematic view of the invention applied to a iour-wheelbrakesystem.

Reierring in detail to the drawings in Fig; I;

the safety device I comprises a cylinder 2 having therein a slidingpiston 3, 'Ifh eleft end of cylinder I has a port 4 connected by pipe 5to the master cylinder shown at .6. in Fig. (i. The other end of 0master CJlihder 6 and the frontbrakes.

If for; example the rear brakes have-a heavy leakage, s ch leakage isprevented from r fering with, the operation of thejront In; as

fluid cannot flow through the piston 3 ina'direction from the mastercylinder to the rear brakes, 60

51018111115. (01. cos-34) w t nsmwba isa reason that if t .e tma zepsrain. 9 th mk it i mnb 'a m jihenew 3 h0 1 i in to a position at t e rightend of cylinder 2 tor the "ere inthat position at a time r steps on thebrake pedal, the

hen. the. are

thebrake linethe pressure at the master cylinder .rtthr u h reassures st I ore. ball valve 'l4-he'ld to its s'eatby a spring !5; The valve lqisarelie f valve and it shuts ofi' the flow when such'flow is indirection from. the master a dei PP wa in st k p in t while pfrn ttirigthe" flowjlunder certain conditions, in the g direction.

n? b a s on vane 14, n its eft tidbits asan ti s' n w 9 of t pi n and isS B C liI'd to the they 29' of the piston by 9%.? thxs q l- Th B ten-head W h s an uni ates with the axial passage 23 which tour a se tinhead 1 sqii t e casin h l bassr iea fllfig" casing'head 24 serves asanabutment for the piston head l fl the ahutrnent at the other side of1d seal uogthr so asto a this b -e af u i' ig ne i a pa i 51? Ta v sis'is; in, he. P n it-ea e with? and with e J around piston I I in adirecti' port II, to maintain the brake lines full at the "a tljierightena t the iyl c t e ist' i k in p i6. preven this a fay al ephamber.lfllar han. hi ou s e valve 14 andsp f n fi. The

. mates, i tht ma ie cylinderport I 6. 'llhepassageL-ZQ is arranged in Te ee r and 1 OfY't-h" 3 right of port I 1, without, thereby, causing thepiston II to drift to the right. This insures an adequate supply ofbrake fluid at all times on the brake side of piston I I. Piston H mayhave a small clearance such as three mils. -Hence, a very slight amountof leakage, due to evaporation or the like, and insufficient to preventthe brakes from operating, can be offset overcoming tendency of piston II to drift to the right. Such incipient leakage, however, is shut off inthe event that a major leak should occur, for the reason that fluidcannot leak around washer 33 when piston II is seated on the end wall28. 'Flow in the opposite direction isprevented by washer 33, as it actsas a hydraulic seal for flow from port I! to I6 to ensure that piston II will travel to the left to the position shown in Fig. 3 where thebrake pedal is released. If washer 33 should seal so tightly as to causepiston II to stick, or if it should .become stuck due to extreme cold orfor any other reason, the brakes will not drag be-.

cause upon releasing the brake pedal and thereby reducing the pressurein the line between the master cylinder and port I6, the pressure in thebrake line, being higher at that time, is relieved by pushing reliefvalve I4 oif its seat to permit fluid to flow from the brakes to themaster cylinder. which is'unlikely to occur, as during normal oper-,ation, when the brake pedal is released, the piston II, due to thehigher pressure in the brake line, is urged to the position shown inFig. 3, for two reasons, where it is operativeto communicate the brakepedal pressure to the brakes. One of these reasons is that the pressureat which the spring I5 operates is intermediate the pressure at whichthe shoe return spring 34 (see Fig. 5) and the piston spring 35 in themaster cylinder operate, bearing in mind that the pressure produced byspring 34 is greater than that produced by spring 35 to return the brakefluid to the master cylinder when the brake pedal is released. The otherreason is that leakage to the right past washer 33 lubricates the pistonand keeps the brake line full of fluid, ensuring its movement to theleft. This leakage is facilitated, even though piston I I is in itsextreme position to the left, by groove 52 extending across the face ofhead I9 of piston ll. 1

The advantage of spring I 5 being stronger than spring 35 is to causethepiston II to move fully to the left before relief valve I4 opens,ensuring that piston II will not drift, or be left in an intermediateposition in the cylinder Ill.

The advantage of having spring I5 weaker than'the shoe. return spring 34is that if the fluid pressure between the brake and the piston II getstoo high, causing the brake to drag, the pressure will be relieved bythe relief valve I4.

In installing the device, the valve 3I is turned to connect port IE toby-pass 30 and the brake line is bled as usual. Then after closing thebrake bleeder valve not shown and opening the bleed passage 40 byremoving plug 4|, the brake pedal is depressed several times, causingpiston I I to move fully to the left or in normal, operating position.With pressure in the passage 30 and the brake line at the right ofpiston II, and with bleed passage 40 open, relief valve I4 permitsbleeding through the piston II. Upon closing passage 40 andturning valve3| to normal operating position shown in Fig. 3, the brakes are inoperating condition.

However, this is an extreme condition Various modifications may be madein the invention without departing from the spirit of the followingclaims.

l. A safety device for a fluid brake, said device comprising a cylinderhaving a port at each of its opposite ends, a piston slidable in saidcylinder and shutting off the flow through one of said ports when saidpiston is at that end of the cylinder, a unilateral fluid seal aroundsaid piston permitting leakage flow towards said one port, andpreventing leakage flow in the opposite direction, a relief passagethrough said piston and a spring pressed relief valve thereforpreventing flow through said passage towards said one port andpermittingflow through said piston in the opposite direction, a by-passaround said piston, a valve for said by-pass, and a bleed passagebetween said by-pass valve and said piston;

2. A safety device for a fluid brake, said device comprising acylinderhaving a port at each of its opposite ends, with a pressure supply firstport and a brake side second port, a manually controlled by-passpassagearound said cylinder connecting said first port with said second port, amanually operated rotary valve controlling said by-pass passage, acompletely hydraulically operated piston slidable in said cylinder forshutting off the flow through said second port in a positive manner whenserious leakage develops or to insure positive brake action where noserious leakage exists, a unilateral fluid seal around said pistonpermitting leakage flow towards said second port and-preventing flow inthe opposite direction thereby insuring positive return of said pistonto static operating position, a relief passage through said piston and aspring pressed relief valve operating at a tension preventing flow inone direction in said relief passage and permitting flow in said reliefpassage in the opposite direction to relieve any excess fluid pressurein said brake side after said piston has been hydraulically urged byrelease movement of fluid to static operating position.

3. A safety device according to claim 2 comprising means providing ableed passage between said rotary valve and said cylinder for bleedingair bubbles from the master cylinder side of said I rotary having athird position disconnecting said master cylinder from both sides ofsaid piston.

DAVID R. HERRIOT'I.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,633,114 Loose June 21, 19271,905,077 Walker Apr. 25, 1933 2,024,042 Jance Dec. 10, 1935 2,095,560-

Vickers Oct. 12, 1937

